Solid state flow control devices are in high demand for moderate to high flow speeds. Such devices can have several important applications. Current solid state flow control devices operate using arc filament and/or arc heating flow control methods. These methods require a high amount of energy and lead to high manufacturing costs.
The generation of plasma due to electrical input has important applications. The basic mechanisms inherent in non-equilibrium discharges such as obtained through DC, RF, or microwave excitation have also been utilized for ionization purposes, so as to increase the conductivity of air for further control with ponderomotive forces generated with an imposed magnetic field. Dielectric barrier discharge (DBD) involves one dielectric coated electrode that is typically exposed at the surface to the surrounding atmosphere, while another electrode is embedded inside a layer of insulator. The emission of UV light as well as chemical processes in surface plasmas is suitable for decontamination in a short timescale and using very low power and heat.
Dielectric barrier plasma discharge at atmospheric pressure (APDBD) has the potential to become a new practical and effective method of sterilization. Sterilization technology has broad applications, from medical devices to food preparation equipment. Products that could self-sterilize after being used could save lives by diminishing accidental exposure of users to infectious diseases and contaminated materials. Conventional sterilization methods, such as autoclaving, use high pressure and temperature to attempt to kill bacteria. Autoclaving is widely used in hospital settings and can be effective. However, it requires long sterilization times (˜20-40 min), longer standing times, and a large infrastructure. Among other techniques used are dry heat ovens, use of chemical agents, gamma ray irradiation, and UV sterilization. Each of these requires expensive infrastructure and long periods of time to achieve complete sterilization.
When plasma is generated, there are radicals that are formed. These can include ozone, heat, and UV light. The combination of these radicals makes possible the process of sterilization via plasma generation. Traditionally, in plasma discharge, a DC voltage potential is placed across two electrodes. If the voltage potential is gradually increased, at the breakdown voltage VB, the current and the amount of excitation of the neutral gas becomes large enough to produce a visible plasma. According to Paschen's law, the breakdown voltage for a particular gas depends on the product (p×d) of the gas pressure and the distance between the electrodes. For any gas there is unique p×d value referred to as the Stoletow point where volumetric ionization is the maximum. The Stoletow point for air requires a minimum VB=360 V and p×d=5.7 Torr-mm.
Near atmospheric pressure, the allowable electrode spacing necessary for maximum volumetric ionization is d=7.7 μm. In some applications, for example in high-speed air vehicles, this is an impractical limitation. A solution to this limitation comes from the recent development of RF glow discharge using an AC voltage potential across the electrodes. The frequency of the current must be such that within a period of the a.c. cycle, electrons must travel to the electrodes and generate a charge, while the heavier ions cannot. Based on reported experiments [2] in air or other gases at 760±25 torr, a homogeneous glow can be maintained at 3 to 20 kHz RF and rms electrode voltage between 2 to 15 kV. A critical criterion for such discharge in air is to meet the electric field requirement of about 30 kV/cm. While the voltage is high, only a few milliamps current is required to sustain a RF driven barrier discharge.
Power supply units that drive dielectric barrier discharge devices like plasma actuators and plasma sterilization devices are heavy and bulky weighing several kilograms occupying several square feet of footprint.
A power amplifier commonly used in single-load applications is a full bridge rectifier. The design consists of a transformer being used at resonance with the load. However, it consists of 4 transistors and large passive components, making it bulky. This system can be used for single-load applications.
Ben-Yaakov and Peretz disclosed a power supply system using a feedback mechanism to achieve stability and a self-tuned resonant system (Ben-Yaakov and Peretz, A Self-Adjusting Sinusoidal Power Source Suitable for Driving Capacitive Loads, IEEE Transactions on Power Electronics, Vol. 21, No. 4, July 2006). Also, Alonso et al. disclosed a power supply for ozone generation (Alonso et al., Low-Power High-Voltage High-Frequency Power Supply for Ozone Generation, IEEE Transactions on Industry Applications, Vol. 40, No. 2, March/April 2004). However, these designs are not efficient and do not produce power outputs high enough for plasma generation.